Patent Application
20060191352
The present invention is in the field of science lab equipment. More specifically this invention relates to measuring the strength and deflection of a sample truss, to aid in learning about truss structures and strengths.
When teaching about trusses, such as various truss structures and how they differ in load bearing ability, it is useful to have a hands on experiment which could show this. Testing could be used to replicate a bridge structure, or to explore vector addition. Thus an apparatus is desired which would demonstrate this in a classroom setting.
An educational device to measure the strength and deflection of a sample truss comprises a mounting base having opposing posts, an adjustable sliding force plate, a load clip, a pulling means, a force measuring means, and a deflection measuring means. The truss has a longitudinal side and an opposing side with a load point, and a first end and an opposing second end. The truss is laid on the sliding force plate such that the longitudinal side is against the opposing posts, wherein one post is at the first end and one post is at the second end. The load clip is mounted on the sliding force plate, and centered relative to the opposing posts, such that when the truss is placed on the sliding force plate, the load clip is against the truss load point. The pulling means functions to pull the load clip against the truss load point, which in turn pulls the truss first longitudinal side against the opposing posts, causing a load on the truss. A force measuring means is then used for measuring the load caused by the pulling means, and a deflection measuring means is used for measuring the deflection of the truss caused by the pulling means.
Various aspects of the invention are presented in
According to an aspect of the invention, the force plate 15 further comprises adjustment slots 17 for attachment of the load clip 16 at various locations to allow for different sized trusses.
According to an aspect of the invention, the force measuring means 14 is a strain gage. The strain gage provides an analog signal, which is sent to a computing and display device through a computer interface 50. There the signal may be converted and recorded. In a preferred embodiment of the invention, the strain gage analog signal is routed through a PC card 66 which converts the signal to digital before it reaches the computer interface 50.
According to a further aspect of the invention, the pulling means 30 is a crank 18 and screw 24 combination, wherein turning the crank 18 turns the screw 24 which in turn pulls the adjustable sliding force plate 15. A retainer ring 19 is used to retain the screw in the proper position, such that all the motion caused by turning the crank results in motion in the desired direction.
According to a further aspect of the invention, the strain gage 14 is located between the force plate 15 and the pulling means 30, such that the force measured by the strain gage 14 corresponds to the load on the truss 13.
According to an aspect of the invention, the pulling means 30 operates by pulling a slide block 12. The slide block 12 is slidably mounted to the base 10 by screws 64 in slots 62. The slide block 12 has a U-shaped cut out 40. This U-shaped cut out 40 leaves a leg 42 at the end of the slide block 12. Force plate 15 has a pulling slot 43, sized to accommodate the slide block leg 42. Thus the slide block leg 42 is inserted into the force plate pulling slot 43. Thus the pulling mechanism 30 pulls the slide block 12, which by leg 42 in pulling slot 43 pulls the force plate 15.
In a preferred embodiment of the invention, there is also a pressure plate 65 which is sized to fit in the pulling slot 43. The measuring means 14 sits between the slide block leg 42 and the pressure plate 65, such that when the slide block leg 42 pulls the force plate 15, it also presses the measuring means 14 against the pressure plate 65.
In a preferred embodiment of the invention, the deflection measuring means 20 is an encoder which records the turns made by the crank 18 and screw 24, and converts this to distance using the pitch of the screw thread. This encoder may also send a digital signal to a computer through a computer interface 50, thus allowing for conversion and recording of the signal.
In a further preferred embodiment, there is a cover plate 21, for covering the truss 13 while it is being deflected. This is useful to help restrain the truss 13 in the test position, and keep it from pulling upward as force is applied. It is also a useful safety cover in case the breaking truss 13 sends flying fragments.
According to another aspect of the invention, there is a support plate 26, wherein the support plate 26 supports the force plate 15 and the truss 13.
